Superabsorbent polymers (SAPs, or superabsorbent resins) are synthetic polymer materials that are able to absorb about 500 to 1000 times their own weight in moisture. Such superabsorbent polymers have begun to be used in real-world applications for sanitary items, and are currently being widely utilized not only in hygiene products, such as disposable baby diapers and the like, but also in soil conditioners for gardening applications, water stopping agents for civil engineering and construction applications, sheets for raising seedlings, freshness preservatives for food distribution, fomentation materials, etc.
Such a superabsorbent polymer may be prepared through reverse-phase suspension polymerization or aqueous polymerization. A hydrogel polymer obtained through a polymerization reaction is typically dried and then ground, and the powdered product thereof is commercially available. As such, in the process of pulverizing the dried polymer, fine powder having a particle size of about 150 μm or less, falling out of the normal particle size range, is generated. This fine powder cannot be sold as a normal product. When superabsorbent polymer particles containing such fine powder are applied to products, they may move before use or may exhibit deteriorated properties.
Hence, this fine powder is excluded from the final polymer product or is subjected to a regranulation process for agglomerating fines so as to fall within the normal particle size range. As such, the regranulated fine-powder has to possess high agglomeration strength so as not to deagglomerate again. Typically, in order to increase agglomeration strength, a regranulation process is performed in a wet state. In this regard, Korean Patent Application Publication No. 2014-0063457 discloses a method of preparing a superabsorbent polymer, which includes forming a fine-powder regranulate using only fine powder and water, without the use of additives, but is problematic because the properties of this superabsorbent polymer may deteriorate compared to a superabsorbent polymer without the use of fine powder.